This invention relates generally to wheelchairs and more particularly concerns wheelchair seats.
Pressure sores are a major problem for many wheelchair patients. According to David Springer in Home Health Care Dealer Provider Magazine, “Pressure ulcers and related co-morbidities constitute the greatest impairment in quality of life, increase in expenses for care, and extended hospital stay for those requiring wheelchairs as their primary mode of locomotion.” Pressure sores can develop quickly. The Merck Manual of Diagnosis and Therapy states, “In an immobilized patient, severe pressure can impair local circulation in less than three hours, causing local tissue anoxia that, if unrelieved, progresses to necrosis of the skin and subcutaneous tissues. Moisture (e.g., from perspiration or incontinence) leads to tissue maceration and predisposes to pressure sores.” Moisture and pressure are the two most significant factors in the occurrence of pressure sores. In Drugs Aging, J. B. Young says, “It has been estimated that the United States spends five billion dollars annually on the treatment of pressure sores.”
One major strategy for preventing pressure sores in wheelchair occupants is to distribute pressure as evenly as possible over the entire interface area between the seated individual and the wheelchair. In order to determine the most effective distribution of pressure, an industry accepted mapping system uses a 36 by 36 cell matrix of 1,296 pressure sensing transducer to determine the pressure pattern imposed on a seat by a wheelchair occupant. The test gives a computer screen visual of the cells to which pressure is applied and the magnitude of the pressure applied to each cell. Common areas where pressure sores develop include the soft tissue overlying the ischial tuberosities and coccyx, the former being the most common. These bony prominences cause acute areas of pressure in almost every seated individual, but this problem is exacerbated for wheelchair patients, and especially elderly wheelchair occupants. Because wheelchair patients are seated for extended periods of time, and do not tend to move around or shift in their seats often, the risk of pressure sores caused by unrelieved constant pressure and the buildup of moisture from perspiration is great. Circulation difficulties and poor seating posture further increase the risk of pressure sores. Furthermore, a wheelchair seat with perforations allows moisture and the heat which precedes moisture vapor to be exchanged with surrounding air. However, simple perforated seats do not provide suitable pressure distribution and do not fold, so the wheelchair is not as easily portable as a standard wheelchair.
One common method of reducing acute pressure areas for wheelchair patients is the use of seat cushions, which compress under bony prominences and/or offer more firm support in regions at less risk for developing pressure sores, such as the posterior thighs. While cushions of this type do lessen the load on sensitive areas of the skin, they do not always relieve enough pressure to encourage adequate circulation, nor do they always encourage good seating posture in wheelchair patients. Further, most cushions facilitate rather than minimize the occurrence and retention of moisture from perspiration at the seat interface because they use fabrics which do not breathe and because they increase the surface area in contact with the wheelchair patient. Seat cushions also have other incidental negatives such as adding weight to the chair and making transport of the chair more inconvenient. Added weight makes mobility more difficult for persons with impaired upper body strength. For active wheelchair users who are in and out of vehicles often, it is not always convenient to transport and handle a seat cushion in addition to the wheelchair itself.
Furthermore, seat cushions are not always available or practical. In many nursing homes and long term care facilities, wheelchairs are provided, but cushions are not provided. Most wheelchairs fold for ease of transport, but the cushion must be removed when the wheelchair is folded. Some cushions are contoured to predispose the pressure load to specific regions, usually the posterior thighs. When cushions are removed and then returned to wheelchair seats, they are sometimes inadvertently rotated so the orientation is improper and the pressure problem is actually aggravated for the wheelchair patient.
Another method of reducing acute pressure areas for wheelchair patients is the use of active pneumatic or hydraulic systems to control cushion pressure. Such systems, as exemplified by U.S. Pat. No. 6,092,249 to Kamen et al, require fluid reservoirs, pressure sources and regulators and pneumatically or hydraulically discrete chambers, all of which contribute to higher cost, greater weight, less convenience and burdensome maintenance while offering no relief for ventilation problems.
It is, therefore, an object of this invention to provide a wheelchair seat which helps prevent pressure sores from occurring. Another object of this invention is to provide a wheelchair seat which allows pressure to be more evenly distributed over its surface. A further object of this invention is to provide a wheelchair seat which reduces acute pressure areas for wheelchair patients. Yet another object of this invention is to provide a wheelchair seat which facilitates the exchange of moisture and moisture vapor with the surrounding air. It is also an object of this invention to provide a wheelchair seat which encourages adequate circulation in wheelchair patients. Still another object of this invention is to provide a wheelchair seat which provides good seating posture in wheelchair patients. An additional object of this invention is to provide a wheelchair seat which does not significantly increase the weight of a wheelchair. Another object of this invention is to provide a wheelchair seat which does not exacerbate the inconvenience associated with transporting a wheelchair. A further object of this invention is to provide a wheelchair seat which is easily adjusted in the event of a change of occupants. Yet another object of this invention is to provide a wheelchair seat which requires no pneumatic or hydraulic systems. It is also an object of this invention to provide a wheelchair seat which requires little maintenance.